1. Field of the Invention
The invention concerns a coordinate measuring apparatus for measuring workpiece geometries with movable traverse axes and having one or several sensors for recording measuring points on the workpiece surfaces. The invention also concerns a process for measuring workpiece geometries with a coordinate measuring apparatus with movable transverse axes and having one or several sensors for recording measuring points on the workpiece surfaces.
2. Description of Related Art
Coordinate measuring apparatus are understood to be measuring apparatus having one or several mechanically movable axes for measuring geometric properties of workpieces or measuring objects. These coordinate measuring apparatus are equipped with sensors for recording geometric measuring points on the workpiece surfaces. The prior art encompasses predominantly coordinate measuring apparatus with purely tactile sensors, that is, the measuring point is generated by contact of the workpiece surface with a tactile sensor. Coordinate measuring apparatus with optical sensors are also known, in which the measuring points are determined by means of optoelectronic image processing or a laser proximity sensor. Coordinate measuring apparatus are also known in which some of these sensors are mutually combined, thus providing expanded options for the user.
An overview of coordinate measuring technology is provided in the publications DE.Z.: The Library of Technology, Coordinate Measuring Technology in Industrial Application, Modern Industry Publishers, Volume 203 (ISBN 3-478-93212-2) and DE.Z.: The Library of Technology, Multisensor Coordinate Measuring Technology, Modern Industry Publishers, Volume 248 (ISBN 3-478-93290-4).
The circumstance is repeatedly encountered in which the customarily used coordinate measuring apparatus is not optimally configured for the respective measuring task, so that as a consequence several apparatus of different designs are required.
It is the object of the invention to further develop a coordinate measuring apparatus as well as a process for measuring workpiece geometries with a coordinate measuring apparatus in such a way that an optimal configuration for the respective measuring task is ensured, so that basically several apparatus of different design are required.
The object is attained according to the invention by equipping a coordinate measuring apparatus with all the sensors required for attaining the measuring object. These can be selectively installed or uninstalled or automatically exchanged during operation via corresponding sensor exchange systems. With this, a flexible measurement of complex workpiece geometries is possible. It is, of course, likewise possible to install a corresponding number of selected sensors on the apparatus and to measure the workpieces with this configuration.
A coordinate measuring apparatus for measuring workpiece geometries with movable transverse axes and having one or several sensors for recording the measuring points on the workpiece surfaces is proposed, wherein an image processing sensor and/or a switching scanning system and/or a measuring scanning system and/or a laser proximity sensor integrated into the image processing sensor and/or a separate laser proximity sensor and/or a white light interferometer and/or a tactile/optical sensing device, in which the position of the molded scanning element is directly determined by means of an image processing sensor, and/or a punctiform working interferometer sensor and/or a punctiform working interferometer sensor with an integrated rotational axis and/or a punctiform working interferometer sensor with a bent viewing direction, and/or an X-ray sensor and/or a chromatic focus sensor and/or a confocal scanning measuring head is installed as the sensor. Herein, the type or number of sensors used is designed for each respective measuring task.
Accordingly, a process for measuring workpiece geometries with a coordinate measuring apparatus with movable transverse axes and having one or several sensors for recording measuring points on the workpiece surface is characterized in that an image processing sensor and/or a switching scanning system and/or a measuring scanning system and/or a laser proximity sensor integrated in the image processing sensor and/or a separate laser proximity sensor and/or a white light interferometer and/or a tactile/optical sensing device, in which the position of the molded scanning element is directly determined by means of an image processing sensor, and/or a punctiform working interferometer sensor and/or a punctiform working interferometer sensor with an integrated rotational axis and/or a punctiform working interferometer sensor with an angular viewing direction, and/or an X-ray sensor and/or a chromatic focus sensor and/or a confocal scanning measuring head is installed as the sensor, wherein the type or number of sensors used can be selected in accordance with the respective measuring task.
Further detail problems occur with the design of such a coordinate measuring apparatus, which are beyond the above-described basic object. These will be described in the following, and solutions for solving these problems will be disclosed.
When applying image processing sensors in coordinate measuring apparatus, it is necessary for the user to set different magnifications. This is contradicted by the requirement of optical systems having optimized costs as well as high imaging quality, which are very difficult to achieve with the otherwise required zoom optic. This can be solved, however, on the basis of an idea of the invention, which will be further developed independently, by selecting a camera for the imaging processing sensor that has a greater resolution (pixel number) than the resolution of the monitor used or the monitor section used for the image representation. The camera can also be equipped with optional access to specific sections of the overall image. It is then possible to represent only one section of the overall image in the live image or observed image of the coordinate measuring apparatus, which is enlarged to the format of the respective display window or monitor. As a result, the user is provided with the possibility of selecting zoomed-in sections of the image according to his/her own ideas. The magnification between the measured object and the monitor image can be controlled by changing the selected section of the camera image by means of the software or displaying the live image in the same way. This can also be operated if required by means of a rotary knob, which is integrated into the control system of the coordinate measuring apparatus, or via a software controller. It is also possible to display the image or the image section only with a low resolution when a high resolution camera is used, but using the full resolution of the camera for digital image processing in the background in order to increase the accuracy. The actual optical magnification of the image optic of the image processing is herein relatively low (typically one time, at the most however 5 times), and the optical effect of a higher resolution is achieved by merely representing a section of the high resolution camera image on the low resolution monitor.
An enhancement of the above-described mode of operation consists in integrating several, but at least two, cameras via minor systems in an optical beam path and utilizing the same imaging objective. A laser proximity sensor can be integrated, in addition, and the same imaging objective can likewise be utilized. It is possible in this way to realize different magnifications for the user by selecting different interfaces or different cameras with different chip sizes and the same pixel number or with different pixel numbers and the same chip size, or both. It is likewise possible to additionally integrate herein a laser proximity sensor in the beam path, which also utilizes the same imaging objective via mirror systems. If the magnification ranges achieved by selecting different camera chips are still not sufficient, it is moreover possible to integrate for each camera a corresponding additional magnification or additional reduction as an optical component in the camera beam path.
In order to prevent different illumination intensities from occurring in different cameras with a uniform illumination of the measuring objective, which lead to difficulties in the image evaluation, the optical splitters (for example, a minor), which split the beam paths for the different cameras, are configured in such a way that all cameras receive the same proportionate light intensity. This is achieved by selecting corresponding degrees of reflection or transmission for the optical splitters that are used, especially beam splitters. In addition, this system can likewise be expanded by means of an integrated bright field incident light beam path. This bright field incident light beam path is likewise realized via a correspondingly dimensioned optical splitter, such as a beam splitter.
A particular problem consists in that the selected display resolution is not an integral multiple or an integral divider of the selected image recording resolution. An adaptation of resolution, one to the other, can be carried out by resampling from the image taken with a high resolution camera. A required number of image points corresponding to the resolution of the evaluation or display range are calculated.
Another problem in the use of known coordinate measuring apparatus consists in the fact that once the programs for measuring workpieces have been created, they will then be subsequently modified, or subsequent features from the already obtained measuring results will be generated. This is not possible in accordance with the current state of the art, since the accordingly corresponding technology data are no longer available. The problem is solved by the invention by recording and storing the measuring points or video images or X-ray images measured with one or several sensors of the coordinate measuring apparatus as well as their corresponding positions and other technology parameters, such as the default value of the utilized illumination systems, light intensity, et cetera of the coordinate measuring apparatus during the measuring sequence, and making these available for a subsequent evaluation. Similarly to this described mode of operation, it is also possible to separately measure several partial images of a measuring object with the image processing sensor and to join these to form an overall image of the overall measuring object or an overall image consisting of the partial sections of the overall measuring object. This image can be stored and later evaluated at a separate workstation. For this purpose, the calibration parameters of the coordinate measuring apparatus used for recording the image are likewise stored and newly utilized with the evaluation software. An offline raster scanning is made possible.
In a modification of the above-described mode of operation, it is likewise possible to store the entire measuring sequence, including the operating position of the coordinate measuring apparatus and/or the images of the image processing sensor and/or the images of the X-ray sensor and/or the scanning points of the tactile sensor and/or the scanning points of the laser sensor and/or further technology parameters, and thus make these available for a subsequent evaluation. During the subsequent evaluation, new measuring results can be generated from the available measuring points and technology parameters, and these can also be checked directly at the measuring apparatus by including the measuring apparatus, and the actual measuring programs for the application on further measuring objectives can also be optimized and modified.
It is provided that when using an image processing sensor for the case in which the visual field of the camera is insufficient to record at one time a defined area of the measuring object by selecting the desired evaluation range (image processing window), the image can be formed from several partial images and then shown to the user as a measured image that is mad available for evaluation.
A frequently occurring problem consists in the fact that these apparatus must frequently be operated by inexperienced operators. In the ideal case, the measuring objects should be simply placed on the coordinate measuring apparatus and the start button should be pushed. The problem consists in that the coordinate measuring apparatus must first be shown where the actual measuring object is located, in order to able to implement the CNC program within the workpiece coordinates of the coordinate measuring apparatus. As an independent invention, the following process is proposed: After placing the workpiece on the coordinate measuring apparatus, a search for the measuring objective within the measuring area of the coordinate measuring apparatus is carried out by driving a sensor, especially an image processing sensor, over a straight-line, spiral-shaped, meander-shaped, circular shaped, stochastic or otherwise shaped search path, until the existence of a measuring object is detected.
A scanning of the outer contour is carried out in a second process step, starting at the starting point generated by the detection of the measuring object (contour tracking for the detection of the outer geometry and position of the measuring object).
In a third process step, the recording of the measuring points located within this outer contour is optionally performed using one of the selectively available sensors of the coordinate measuring apparatus, for example, by rastering with the image processing sensor or scanning with the tactile sensor. The measuring points obtained in this way can then be forwarded for further evaluation in accordance with the testing plan. It is also possible to subsequently measure canonical geometric elements within the known workpiece position, or to simply utilize the first measured contour points to align the workpiece in the workpiece coordinates and then measure canonical geometric elements and features, such as angles and distances.
A further problem when using coordinate measuring apparatus, especially in those with image processing sensors, consists in the fact that the different illumination sources have non-linear characteristics, that is, the default value of the illumination intensity indicated on the computer software is not connected with a linear interrelationship with the actual illumination intensity of the illumination system. This leads to the fact, among other things, that different measuring objects cannot be correctly measured or programs cannot be transferred form one apparatus to the other without difficulty. In order to solve this problem, it is proposed according to the invention to record the characteristics of the illumination devices of the image processing sensor system of the coordinate measuring apparatus, that is, recording the dependency of the illumination intensity on the default values of the operator interface of the measuring device by measuring the intensity at the corresponding default value with the image processing sensors. The corresponding measuring results are stored as characteristic results in the computer of the measuring apparatus. As an alternative, it is also possible to store these measured values in a so-called light box, which carries out the control of the illumination intensity during the operation of the coordinate measuring apparatus. If this light characteristic measurement is carried out on a calibrated reference object or at least for several apparatus on a standard calibration object, it becomes possible in this way to balance the apparatus in their behavior toward the outside, that is, in their behavior with reference to the dependency between the default light value and the physical illumination value, and thus to ensure the program transferability of different apparatus. In order to facilitate the operation of the apparatus, it is practical to correct the characteristic in such a way that a linearity is preexistent for the operator, that is, the previously measured characteristic is taken into consideration in such a way for the correction calculation during the operation of the coordinate measuring apparatus that it appears that a linear characteristic is available for the operator, that is, the default value and the illumination intensity then follow a linear interrelation. The increase of this linear characteristic can then be balanced for several apparatus by means of a simple correction factor.
Based on the above-described linearization of the illumination device characteristics in the coordinate measuring apparatus, it is possible to solve the problem that measuring objects of different brightness cannot be measured without problems with the same illumination setting, since the illumination of the measuring object is not correctly provided. This is attained in accordance with the invention by carrying out the following process steps:
While implementing automatic programs for measuring parts with different reflection intensities, the default values predetermined in the program are first adjusted for the illumination intensities of the different illumination sources. In a second step, the illumination intensity, which is influenced by the reflection behavior of the workpiece, is tested using the image processing sensor, and it is monitored whether the measured value corresponds to the stored desired value or default value. If the deviation between desired and actual value exceeds a fixed threshold value, the default value of the illumination intensity is linearly corrected and newly adjusted according to the previously recorded light characteristic of the illumination system. The result of this is that the desired light intensity, as stored in the program, is reflected by the measuring object. The desired object feature is then measured. This procedure is repeated according to the number of image sections that the coordinate measuring apparatus requires for solving the measurement task. The advantage of this mode of operation as compared with conventional light control systems is that only two images of the measuring object must be recorded in this control process, thus a very fast light control can be realized.
According to the above-described mode of operation, it is likewise possible to store several characteristic sets for the coordinate measuring apparatus, which correspond to the behavior of further similar coordinate measuring apparatus, but with different light characteristics. Measuring programs of older or foreign manufacturers can thus also be utilized.
With coordinate measuring apparatus, it is possible to scan contours of workpiece surfaces. This can be realized with one sensor or with the combined operation of several sensors. If an evaluation of the contours is carried out by comparing these with desired contours from, for example, CAD files, it is necessary to internally superimpose desired and actual computers in order to realize a graphic comparison. This cannot be accomplished by means of a simple offset of the relative position or a rotation of the relative position especially with flexible or elastic parts, since the parts are elastically deformed. This problem is solved by proceeding according to the method having an inventive content, which is described in the following. With the best adaptation between desired and actual contour, aside from the relative position change between the desired and actual contour per se, the length of the contour sections corresponding to the desired length is also modified, while maintaining the curvature, or alternatively, the contour curvature is modified, while maintaining the contour length at the actual contour, in such a way that an optimal coverage is achieved with the desired contour. If the parts having distinguished geometric features are difficult to test due to their elasticity or deformation, this procedure can be reinforced by carrying out the adaptation between the actual and desired contours on a group of actual and desired contours to individually distinguished features, such as the intersection points of contours or circular structures or other recurring structures, thus generating a distortion of the actual contour for an optimal coverage with the desired contour. This is also possible in a similar way with cylindrical parts, in which the contours measured on the cylinder surface are partially rotated or screwed on the cylinder jacket surface in order to produce an optimal coverage between desired and actual contours. This mode of operation is suitable in particular for measuring the customary stents used in medicine. The above-described method is also possible in a similar reversed mode of operation, that is, an adaptation of the desired to the actual geometry.
In order to achieve a metrologically suitable evaluation of the desired to actual comparison, it is practical to optimize the adaptation not toward a minimization of the deviation between the desired and actual contour, but toward a minimization of the tolerance zone utilization. In practice, however, the tolerances for the measurement of the parts are generally predetermined as measurement, shape and/or position tolerances in the form of printed drawings or CAD drawings. The conversion of these tolerances into corresponding tolerance zones is to be achieved by means of the coordinate measuring apparatus. This object is attained according to the invention by storing algorithms in the coordinate measuring apparatus, which implement an automatic conversion of the measurement, shape and/or position tolerances into tolerance zones related to the contour sections. In the simplest case, one standard overall tolerance of the contour section is obtained for several tolerances. For more complicated tolerances, however, it is also possible that this may not be realizable. In this case, a multiple evaluation is automatically carried out for the different tolerance situations in the coordinate measuring apparatus. For this purpose, several tolerance zones are assigned to each desired or actual contour segment. Automatic successive evaluations are then performed on several desired or actual contour areas combined in groups and/or the desired and actual contours of the complete workpiece for respectively several different position, measurement and/or shape tolerance situations. As an option, the unfavorable result of the different desired to actual comparisons can be displayed at the end of the evaluation for each desired or actual contour segment with the aid of the different tolerance zones.
It is frequently the problem when an image processing with autofocusing sensors is used that the height of partially transparent layers is to be measured. In order to solve this problem, it is proposed according to the invention to simultaneously generate autofocus points on several semi-transparent layers for several evaluation ranges with the image processing sensor in autofocus mode. This is realized by moving the image processing sensor in the measuring direction while at the same time recording several images. The focus measuring points are calculated according to a contrast criterion within the respectively fixed evaluation ranges.
When using coordinate measuring apparatus in connection with a laser proximity sensor, it is customary to scan contours on workpiece surfaces in a sensor measuring direction, that is, the coordinate measuring apparatus is moved over a predetermined path in a direction that is different from the sensor measuring direction. Under the control of the sensor, the coordinate measuring apparatus is guided in the measuring direction of the sensor within the remaining axis. In practice there is also the task of measuring, for example, a sphere having predefined contour lines. This is not possible using the above-described mode of operation. In order to solve this problem, the invention provides that the position control of the sensor or the position control circuit of the coordinate measuring apparatus is controlled in such a way, in dependence upon the deflection display of the laser proximity sensor, that the deflection of the laser proximity sensor remains constant. The axes of the coordinate measuring apparatus are moved herein perpendicular or nearly perpendicular to the measuring direction of the laser proximity sensor. According to the marginal condition, it is taken into consideration that the measuring points of the laser proximity sensor are located within a predefined section plane. It is thus possible to scan contour lines on the measuring object. The laser proximity sensor is moved over a path in which the distance between sensor and object is equal.
A further problem when using coordinate measuring apparatus consists in the fact that the measuring objects must be measured from different sides. If, however, the position of the measuring object is changed within the coordinate measuring apparatus, the reference of the measuring points between each other is lost, and a mutual evaluation of the measuring points is no longer possible. This problem is solved according to the invention by directly applying either reference features of the measuring object itself or additionally applied reference features (preferably spheres) on the measuring object or on a measuring object supporting frame. The mode of operation for measuring with the coordinate measuring apparatus is as follows:                1. Measuring the position of one or several, preferably three reference marks, in particular spheres, on the measuring object or fixedly allocated thereon;        2. Storing the position in the computer of the coordinate measuring apparatus;        3. Measuring any desired points on the measuring object, which are accessible by means of one or several sensors;        4. Changing the position of the measuring object within the measuring volume of the coordinate measuring apparatus manually or by means of an integrated rotational axis or rotational pivoting axis;        5. Again measuring the reference marks;        6. Internally balancing the respective reference marks so that a minimized offset is present between them in the software;        7. Measuring further points on the measuring object with one or several sensors of the coordinate measuring apparatus;        8. Repeating the above-mentioned procedures any number of times;        9. Jointly evaluating all the measuring points of the measuring object within a coordinate system recorded during the above-described measuring cycle.        
The advantage of this mode of operation is that the accuracy of the rotary pivoting axis used for the rotation or rotary pivoting of the measuring object is not suggested in the measuring result. The measured position values of the rotary axis or rotary pivoting axis can of course also be utilized for the evaluation. It is likewise possible to measure the reference marks (preferably spheres) with a sensor and to accordingly carry out the measurement on the workpiece with a corresponding other one.
Coordinate measuring apparatus with different sensors also selectively have, among other things, sensors with an optotactile sensing device. Therein, the determination of the position of the molded scanning element (sphere, cylinder) is carried out by means of an image processing sensor (WO-A-98/157121). A problem is presented by the need to adjust this sensor to the position of the scanning sphere. This is realized according to the invention by additionally arranging an adjustment unit, which makes possible a relative adjustment between the molded scanning element (scanning sphere including scanning pin and holder) and the image processing sensor, on the coordinate axis that carries the sensor. For example, an automatic focusing of the molded scanning element is then possible in relation to the image processing sensor via an autofocusing process.
If highly accurate measurements are carried out with tactile sensors, the problem can occur that the geometric quality of the molded scanning element (sphere, cylinder or the like) is worse than the required measurement inaccuracy. This leads to unusable measuring results. In order to solve this problem, the invention proposes to measure the geometry of the molded scanning element (for example, sphere, cylinder) in advance at an external measuring location and to automatically take these measured values into consideration as correction values when using the molded scanning element in the coordinate measuring apparatus. As an alternative, it is possible to record the deviation of the actual geometry itself from the ideal desired geometry of the molded scanning element by means of measurements in the utilized coordinate measuring apparatus on a highly accurate calibrated measurement standard (such as a calibration sphere).
An important option for coordinate measuring apparatus is the possibility of exchanging different sensors or scanning pins or optical attachments, among other things. An exchange device can be provided for this purpose according to the invention. In order to prevent a limitation of the measuring volume of the coordinate measuring apparatus due to the placement of the exchange device, it is provided according to the invention to arrange this exchange device on a separate adjustment axis, which drives the exchange device out of the measuring volume when no exchange cycle is planned, and drives the exchange device into the measuring volume when an exchange cycle is planned. This adjustment axis can be configured with a spindle drive. As an alternative, it is possible to work with only 2 stops, against which it is positioned by means of a motor drive. As an alternative, it is possible to determine the 2 positions by means of a linear path measuring system or a speed sensor on the spindle drive.
Coordinate measuring apparatus are generally exposed to different working temperatures at the place where they are installed. If several sensors are mounted on the coordinate measuring apparatus, this leads to thermally induced changes in the positions between the different sensors. This leads to measurement errors. In order to solve this problem, it is proposed according to the invention to measure the temperature of the mechanical components that serve for mounting the different sensors at one or several locations, in order to compensate for defective actions due to temperature fluctuations at the location of installation of the coordinate measuring apparatus, and to take into consideration the expansion of the corresponding mechanical components when calculating the measuring points that are recorded by the different sensors. This means that, for example, when using a sensing device in an image processing sensor, the temperature of the component that connects the two sensors is permanently measured, linked to the linear expansion coefficients of the material utilized for this component, and thus the corrected relative position of the sensor in the coordinate system of the coordinate measuring apparatus is calculated. These corrected values are included in each measurement of measuring points. The above-described temperature compensation is carried out in a typical embodiment by means of a linear multiplication of the measured values by a constant factor, which is influenced by the temperature.
In order to be able to measure a measuring object from several sides during the measuring procedure on a coordinate measuring apparatus, it is practical to clamp the measuring object in a rotational axis and thus rotate it into an optimal position for measurement with the different sensors. In addition to holding the measuring object with the rotational axis, it is also possible to use a corresponding countertip. When the measuring objects are clamped between tips, however, the problem arises that the tensile force of the countertip can lead to deformations of the measuring object. In order to preclude the errors caused by this, it is proposed according to the invention to constantly deform the measuring object or to automatically position the countertip on the measuring object until a predefined force is reached. In this way, the countertip is elastically mounted, so that the correspondingly required force can be determined via a deflection and a corresponding end switch.
A further problem with regard to the use of coordinate measuring apparatus consists in that frequently several contours are to be measured closely together. With the required number, this leads to considerably long measuring times. This problem is solved according to the invention by arranging several tactile sensors of the same kind and different design closely together on a mutual mechanical axis of the coordinate measuring apparatus. It is likewise possible to arrange several of the mentioned sensors on a rotary pivoting unit. With the tactile sensors arranged in this way, the contours of the workpiece surfaces can be simultaneously recorded during the scanning operation. An extensive measurement is carried out in this way. An embodiment variation results according to the invention, which uses only one of the several arranged sensing devices for realizing the scanning operation of the coordinate measuring apparatus (control of the positioning process of the coordinate measuring apparatus based upon the deflection of the sensing device), and operates the other sensing devices merely to (passively) record measured values. These do not contribute to the control of the coordinate measuring apparatus. The control of an optional rotary pivoting unit for the multisensor arrangement can be automatically carried out by means of the difference between the average deflections of the different individual sensing devices. Typical application cases for the mentioned multisensor arrangement are the measurement of tooth flanks, toothed wheels, or the measurement of the shape of cams of camshafts. Several measuring tracks are simultaneously generated during one measuring procedure according to the invention.
When the measurement is carried out with an image processing sensor on the outer edges of workpieces, in particular of rotationally symmetrical cutting tools or cutting plates, there is always the problem that the image processing sensor has to be permanently refocused on the outer edge to be measured. This problem can be solved according to the invention by additionally integrating a laser proximity sensor in the image processing beam path. The laser sensor measures the distance from the image processing sensor to the workpiece surface in the vicinity of the outer edge to be measured, and is connected in such a way to a position control circuit of the coordinate measuring apparatus that an automatic tracking takes place. The image processing sensors are thus permanently focused. The tracking of the workpiece for the focusing operation can alternatively be realized with the Cartesian axes of the coordinate measuring apparatus or also by means of an optional rotational axis (rotation of the workpiece to be measured).
When using image processing sensors in coordinate measuring apparatus, one problem consists in the fact that the number of evaluated images is not sufficient for the required number of measuring points or the total measuring time cannot be sufficiently realized for the requirements. In the state of the art, the camera of the image processing system of the coordinate measuring apparatus is operated in video standard (50 to 60 Hz) and stores and evaluates an image in loose order predetermined by the operator or by means of the program sequence of the coordinate measuring apparatus. In this way, the number of evaluated images is clearly smaller than the number recorded by the camera. As a result, the measuring time is not optimal or the measuring point number is insufficient. In order to solve this problem, it was proposed according to the invention to carry out the evaluation of the image for each image taken by the camera. This means that the evaluation is realized in real time video. In other words, during the time in which the image is being taken by the camera of the image processing system, the calculation of the image evaluation of the previous image is being carried out parallel with and at the same time that the image is being taken by the camera of the image processing system. This procedure is continuously repeated until the entire measuring process has ended. The image evaluation of the image processing sensor is thus carried out in real time video, that is, in the same frequency as the image repeat frequency of the camera. Based on this mode of operation, it is possible to rotate the measuring object with a rotational axis during measurement, and to record and evaluate the latter with the frequency of the camera measuring point on the outer edge of the measuring object for the realization of roundness measurement in real time video.
It is also possible according to the invention to extend the integration time in order to improve the signal to noise ratio of the image processing sensors or X-ray sensors until a sufficiently low signal to noise ratio is available. This means that several successive images are added and the image evaluation is carried out on this added image. This procedure can be automatically controlled by extending the integration time of such a camera until a sufficiently good image can be stored and further processed. The intensity of the image points is herein monitored up to a desired value and enlarged by storing several images.
In the coordinate measuring apparatus according to the invention image processing sensors with laser sensors integrated within the beam path can be used. These beam paths can also be configured as zoom optics. In a further embodiment, the working distance of the zoom optic used can also be adjusted. In the systems used in practice, it is to be expected that the desired optical properties of the integrated laser proximity sensor and the image processing sensor are not available with the same adjustment parameters (working distance/magnification). According to the invention, the aperture and working distance of the zoom optic systems used can be alternatively optimized for the laser sensor or the image processing sensor. This additional optical system can be configured in such a way that the same adjustment parameters (working distance/magnification) are not available for the laser sensor and the image processing sensor. The aperture and working distance of the zoom optic system used can be optimized as an alternative for the laser sensor or the image processing sensor by means of an additional exchangeable optical attachment. This additional optical system can be configured in such a way that it creates optimized conditions for the laser sensor. It is possible to connect this attachment via a magnetic interface to the zoom optic and/or to exchange it via a sensing device exchange station that is otherwise used for tactile sensors.
Different illumination sources, such as bright field, dark field, and dark light, are used when the measurement is carried out with image processing sensors in coordinate measuring apparatus in order to achieve respectively optimal contrast conditions for partial areas of a workpiece to be measured. These illumination sources are varied with regard to their settings, such as intensity, solid angle of the illumination (illumination angle or direction of illumination), or illumination direction, in order to achieve optimal conditions. These parameters are different for partial areas of the object to be measured, which is why it is not possible to optically reproduce the entire object with one illumination setting. In order to preclude this disadvantage, it is proposed according to the invention to record several images, one after the other, using different illumination sources, in order to generate an optimally contrasted image, and to remove from each image the areas with optimal contrast and join these to form a geometrically correct overall image. In detail, it is thus possible to record different images of the same object or object section by using different illumination directions of a dark field illumination and/or different illumination angles of a dark field illumination and/or by using a bright field illumination, and to join the optimally contrasted areas of the individual image to form an overall image. This can then be metrologically evaluated. The described mode of operation can be likewise applied to each individual pixel of the image processing sensor, that is, the pixel with optimal contrast is selected from among the number of individual images for each pixel of the resulting overall image. The contrast of a single pixel is determined by means of the amplitude difference of this pixel with regard to its neighbor in the image.
If the surface contour of workpieces is measured with an autofocusing sensor, the measuring points are usually predetermined by the operator in the teach-in mode. If unknown contours are to be measured in this process, this is only possible with difficulty. This is improved according to the invention by carrying out a scanning procedure on the material surface with an autofocusing sensor in such a way that the expected location of the next measuring point is theoretically calculated from the already measured focus points by interpolation, and can be exactly verified by means of a new autofocus point. If this procedure is repeated several times in succession, a fully automatic scanning is achieved. The number of points to be scanned along one line as well as an area to be scanned on the workpiece or measuring object can be predetermined by the operator. The extrapolation of the next measuring point from the two or more preceding measuring points can be carried out by means of a linear extrapolation. It is further possible to perform this extrapolation via polynomial interpolation of the latest measured two or more points.
If several delimited areas of the image are utilized to determine the focus points during each focusing procedure, a sequence of measuring points can thus be generated during one focusing procedure. If these sequences are placed one after the other, a scanning of complete contours is likewise realized.
When image processing sensors or X-ray tomography sensors are used, the problem arises that areas with strong as well as weak intensities are present within an image, depending on the properties of the measuring object. This is caused by the different reflection or transmission properties of the materials. As a result, only low signals, with the consequent bad signal to noise ratio, are present for the “dark” image areas. However, a stronger illumination or irradiation of the object would lead to an outshining in the brighter areas and should thus be excluded.